I'm confused about surface states in Weyl semimetals. Assume that we have a single pair of Weyl points and the Fermi level turned to this points. In this https://arxiv.org/abs/1301.0330 paper the authors write:
if the Fermi energy is tuned to the Weyl point in the bulk, the bulk states at this energy are only at the projections of the Weyl points to the surface Brillouin zone. Everywhere else, surface states are well defined because they cannot decay into bulk states at the same energy and momentum. As the Weyl point momenta are approached, the surface states penetrate deeper into the bulk.
But I don't understand what they mean, are these surface and bulk states refer to real space or just to momentum space?